DESCRIPTION: Cancer virotherapy is a pragmatic approach with a simple, yet practical, therapeutic mechanism - purposeful conversion of the intrinsic cytolytic property of a virus into targeted killing of malignant cells. Although significant progress has recently been made in this field, a remaining major obstacle is the lack of an efficient means to deliver oncolytic viruses by the systemic route, which is hampering its application in treating metastatic diseases. Key components that affect the delivery efficiency of oncolytic viruses by the systemic route include engulfment of viral particles by the mononuclear phagocyte system (MPS), clearance of virus infection by natural killer (NK) cells, and neutralization of virus infectivity by antiviral antiboies. Additionally, as the systemically delivered viral particles are instantly diluted by the large bloo volume, a delivery strategy that can actively enrich viruses to the tumor site may need to be developed and applied. This project is purposefully designed to develop a series of novel strategies to overcome these major obstacles; primarily, it will use a unique oncolytic virus (FusOn-H2) that was originally constructed in our lab. In aim 1, we will test our hypothesis that genetically coating FusOn-H2 with a don't eat me signal molecule allows the virus to escape the clearance of MPS during systemic delivery. CD47 is a major don't eat me signal molecule. We plan to fuse the extracellular domain of CD47 with a viral glycoprotein to coat the virus and will conduct a series of in vivo experiments to show that genetically coating the virus with CD47 can indeed enhance systemic delivery of virotherapy against metastatic disease. In aim 2, we will test the idea that a chimeric molecule, HER2-Col-Fc, once incorporated into FusOn-H2, can redirect NK cells to attack tumor cells instead of clearing the virus. HER2-Col-Fc contains three key domains: the single chain antibody specific for the tumor antigen HER2, the Fc fragment from IgG and the trimerization domain from collagen. When expressed as a secreted form, this molecule self multimerizes and attaches to HER2-expressing tumor cells as aggregates, which can then efficiently bind to the low affinity Fc receptor (Fc?RIIIA) on NK cells to activate them o kill tumor cells. This simultaneously diverts NK cells from clearing oncolytic virus. In aim 3, we will demonstrate that a novel cell carrier can protect FusOn-H2 as well as actively deliver the virus to tumor sites by the systemic route. In our recent studies, we have generated a novel chimeric antigen receptor that specifically targets tumor neovasculature. T cells engrafted with this receptor (T-eCAR) can specifically attach to and destroy tumor blood vessels. We will test our hypothesis that T-eCAR can function as a perfect cell carrier for systemic delivery of FusOn-H2, as they can protect the virus from the neutralizing antibodies and actively send the virus payload to the tumor site. Although this project is mainly designed to address the obstacles associated with systemic delivery of an oncolytic HSV, most of the strategies can be applied to other oncolytic viruses or to gene delivery vectors in general.